This is a new application requesting four years of funding to study a transgenic mouse line, TG.KD, which has a high incidence of malignant ovarian teratocarcinomas in the hemizygous state. Ovarian teratomas are tumors that originate from female germ cells. They are a common, yet poorly understood neoplasm of women that develops from pluripotential stem cells. The stem cells, embryonal carcinoma (EC) cells, probably arise by an epigenetic mechanism from parthenogenetically activated germ cells, and can differentiate into a wide variety of embryonic tissues to form teratomas. A teratocarcinoma is a malignant form of teratoma that contains undifferentiated EC cells in addition to differentiated derivatives. The primary objective of the proposed research is to isolate the mutated gene at the TG.KD transgene insertion locus and to understand the role of the isolated gene in the development of ovarian teratocarcinomas. Three specific aims are proposed: 1. To test the hypothesis that ovarian teratocarcinomas arise in the TG.KD line as the result of the transgene insertional inactivation or activation of a host gene, transcripts at the transgene integration locus will be identified, cloned, and characterized. 2. To assess when during germ cell development the mutant gene acts, F1 mice will be produced by crossing the TG.KD-bearing FVB/N inbred line to other inbred lines. The resulting teratocarcinomas will be genotyped using heteromorphic markers for the pericentromeric and distal regions of several chromosomes. The distribution of markers relative to that in F1 somatic cells will be used to determine the latest stage of meiosis reached during the formation of the teratocarcinomas. 3. To examine the phenotype of mice homozygous for the TG.KD transgene insertion. While hemizygous TG.KD transgenic mice have a propensity to develop ovarian teratocarcinomas, homozygous mice exhibit a perinatal lethality. Based on the working hypothesis that the same gene mutation underlies both the teratocarcinomas and the perinatal lethality, the phenotype of the homozygous embryos will be examined histologically to provide information regarding the function of the mutated gene.